Endless Cave is located near the top of Azotea Mesa in the foothills of the Guadalupe Mountains of southeast New Mexico. The surrounding country is in the northern portion of the Chihuahuan Desert. The land surface is dry and sparsely covered with cactus and desert grasses. Daytime summer temperatures may reach 120š F, and winter lows can be below 0š F. Late summer thunderstorms bring much needed water to the land and to the underground. During all of these surface temperature and hydrologic fluctuations, the temperature in Endless Cave remains a constant 68š F with a constant humidity of 98%.

Endless Cave is one of several caves on Azotea Mesa, a flat-topped feature whose elevation is 4,200 feet. The cave was formed in Permian period limestone. Two hundred fifty million years ago, the limestone was deposited in a shallow lagoon behind a barrier reef. (The ancient reef was much like today's Great Barrier Reef off the eastern coast of Australia.)

Some gypsum deposits, such as this "commode" in Endless Cave, are useful in determining the origins of caves. Such thick floor deposits are the by-product of the solution of limestone by sulfuric acid.

The caves of the Guadalupe Mountains are thought to have been formed by sulfuric acid rather than the more common solvent of limestone caves, carbonic acid. Scientists believe that ground water combining with hydrogen sulfide from the oil and gas deposits thousands of feet below the cave levels produced the sulfuric acid. The acid is very reactive with limestone and dissolves it quickly, leaving behind gypsum as a byproduct. Many of the caves in the Guadalupe mountains contain vast deposits of gypsum.

Endless Cave has three distinct levels and contains nearly two miles of surveyed passages. Many of the passages are accessible by walking upright, but several sections of the cave require hands-and-knees crawling and wiggling on one's belly for long distances. But diligent exploration pays off when you can finally stand in a spacious cave room filled with the beautiful formations called speleothems, calcium carbonate features deposited by dripping water. Two types of speleothems arestalactitesand stalagmites. (You can remember the difference between them this way: the word "stalactite" is spelled with a "c" in the middle, and these formations cling to the ceiling; the word stalagmite is spelled with a "g," and these grow from the ground.) Other speleothems, such as helictites, soda straws, draperies, flowstone, and popcorn, are also common in Endless Cave.

Stalactites common speleothems decorate the ceiling of Sand Cave, near Carlsbad, New Mexico. Color variations in speleothems are caused by impurities or bacteria picked up by water as it percolates into the cave.

The War Club Room in Endless Cave boasts massive stalagmites.

The cave is home for a summer colony of bats. The bats spend the winter in Mexico and return to the cave in April to bear their young and spend the summer eating insects. They are a great benefit to the local farmers as a sort of "natural insecticide." The colony has at times grown as large as 6,000 bats, and each bats can eat up to 1,000 insects each hour.

Other wildlife species that live in the cave can be found in zones. In the "twilight zone" (yes, there really is such a place! it's the area where natural sunlight filters into the cave) you may find rattlesnakes, mice and other small rodents, ringtail cats, and other temporary users. Further into the cave, you may find smaller wildlife, such as cave crickets, spiders, and beetles. These insects only spend part of their time in the cave and generally go outside to feed at night. Deep in the cave, insect life is totally adapted to the cave environment. They are colorless, and have no eyes. (At such depths, there is complete darkness, so coloration and eyesight would be useless to these creatures.)

Caves often contain the bones of animals that either fell in and could not get out, or became lost in the caves and died. Some such bones are thousands of years old and give paleontologists a record of what kind of animals lived in the caves in the past. Some of the bones that have been found by paleontologists in the caves on Azotea Mesa date back two Ice Ages ago, nearly 50,000 years. Many species, such as camel and certain varieties of ancient bison and bear, are now extinct in North America.

Early man has also used the caves here, and archaeologists have found many of the objects they made and used while they lived here. Arrow points, baskets, sandals, and paintings are some of the artifacts that have been discovered. These artifacts are carefully documented and recorded by the scientists to help us learn as much as we can about those who came before us.

Caves are fascinating places, and contain some very unique and fragile resources. Unfortunately, many of the special things found in caves are not well understood by some cave visitors. Speleothems are broken, bat colonies disturbed, wildlife habitat is polluted, and records of the past are destroyed. Before you enter a cave (always with a trained adult!), read and learn as much as you can so you can help protect these special places and know how to explore them safely.